YITH WooCommerce Cart Messages is an extension designed for those who wish to create custom messages that will be displayed in one or more pages in the website (Product page, Archive page, Cart, and Checkout page). Messages can be displayed at all times or only for specific products in the cart.
Thanks to this integration, each custom message you have created can be shown in the automatic popup (by using YITH WooCommerce Added to Cart Popup) when a product is added to cart.
After installing and activating both plugins, you can create your custom messages in WooCommerce -> YITH Cart Messages. Here, you will find the option Show on “Added to Cart” popup that, if enabled, will allow you to show the message right inside the popup that will open after adding the product to cart.